1. Field of the Invention
This invention generally relates to optical systems and more specifically to endoscopes having an image transfer guide that lies along a curved optical axis.
2. Description of Related Art
Endoscopes have attained great acceptance within the medical community in connection with a number of procedures primarily because they provide a means for performing procedures with minimal patient trauma by enabling a physician to view directly the internal anatomy of a patient. Over the years a number of endoscopes have been developed and have been categorized according to specific applications. Many have specific names including arthroscopes, cystoscopes, proctoscopes, laparoscopes. Industrial endoscopes are often called borescopes.
In whatever form, an endoscope generally comprises an objective lens system at the distal end of the endoscope that forms an image of an object. With medical endoscopes, the object is generally within a patient in some environmental media such as air, water, a saline solution or the like. With industrial endoscopes the object may be located in a remote enclosed volume. An eyepiece or ocular system at the proximal end presents the image for viewing visually, electronically or otherwise externally of the patient or enclosed volume. An image transfer system intermediate the objective and the eyepiece systems transfers the image produced by the objective lens system to the eyepiece system.
Endoscopes are classified by different applications that impose various optical and physical requirements including size of the field of view, image quality, maximum acceptable outer diameters, length and whether the endoscope should be rigid or flexible. Two particular applications for endoscopes to which this invention is particularly adapted are arthroscopes and laryngoscope. Arthroscopic procedures require a relatively thin probe that is inserted into a joint to be examined. The resulting image must have good spatial and contrast resolution to allow a physician to diagnose any injury in the joint being examined, such as the knee, and to undertake appropriate treatment. Typical endoscopes are either forward or downward looking. While forward or obliquely viewing endoscopes can often have a fairly significant field of view, complete diagnosis for damage in the knee joint often requires a wider view than even conventional endoscopes can provide. Different approaches have been taken to improve the imaging of knee joints including the use of a periscope like structure as disclosed in U.S. Letters Pat. No. 5,188,093 to Lafferty et al. In that endoscope a cylindrically shaped rod of a material having a cylindrical gradient refractive index attaches to the distal end of a scope needle that is slidably introduced through the cannula of a catheter or auxiliary lumen of an endoscope. Light reflected from the interior structure of a joint enters the distal base of this rod and is focused onto its proximal base. The image guide is bent near its distal portion to form an angle of about 25.degree. between the distal portion of the image guide and the axis of the probe, so the axis of the rod is not parallel to the probe axis. A fiber optic image guide transfers the image from the distal end of the arthroscope to the proximal end.
U.S. Letters Pat. No. 5,512,034 discloses another version of an endoscopic device with a bent distal tip portion that carries an objective lens. This approach also utilizes a fiber optic image guide to transfer the image formed by the objective lens system to the proximal end of the structure.
As is known, spatial and contrast resolution from fiber optic image guides is inferior to the corresponding image characteristics provided by a properly designed relay lens system. However, typical relay lens systems are rigid structures that lie along a straight optical axis. Viewing off this central axis is accomplished by designing an objective lens that views along a field of view axis that diverges distally from the central endoscope axis. However, these structures limit the amount by which the field of view axis can diverge from the central endoscope axis. It has been found that many arthroscope procedures could benefit from a greater angle of divergence than possible with conventional relay systems, relay systems being preferred because of their improved optical characteristics.
For similar reasons laryngoscopes are also typically rigid straight endoscopes that comprise relay lens systems so that the image viewed in the larynx is of high quality. It would be helpful if a laryngoscope could be curved to more closely match the curved passage from the mount to the larynx.